The late comedian George Carlin drew up a list of seven words you can never say on broadcast television. No one has ever tried to enumerate the combinations of letters and numbers that can’t be printed on a government-issued vanity license plate.

Policing that seven-letter medium falls to a group of state motor vehicle employees who have a knack for solving word puzzles, a Mencken-like command of modern slang, and the disposition of a barroom bouncer.